Electroluminescent display systems

ABSTRACT

A display system including a display screen having at least two component panels, one of the panels having a plurality of elements for emitting light when activated and the other panel having a layer comprising strips of material between two sets of conductive electrodes so that when an element of the first panel is caused to emit light, a potential is applied to conductive elements in the first and second electrodes of the second panel to activate the corresponding portion of the layer and transmit light through that portion whilst preventing light from passing through other portions of the layer. Circuits are provided to operate the display panel.

United States Patent Inventor Philip C. Norem New York, N.Y.

Appl. No. 631,846

Filed Apr. 12, 1967 Patented Feb. 23, 1971 Assignee Autotelic Industries Limited Fort Erie, Ontario, Canada ELECTROLUMINESCENT DISPLAY SYSTEMS 16 Claims, 19 Drawing Figs.

(8), 5.4 (EL), 7.3 (D), 7.5 (D), 6 (A), 6 (LMS); 315/169 (TV); 313/108 (B&D); 250/213 Primary Examiner-Robert L. Richardson Attorney-Jacobi, Davidson & Kleeman ABSTRACT: A display system including a display screen having at least two component panels, one of the panels having a plurality of elements for emitting light when activated and the other panel having a layer comprising strips of material between two sets of conductive electrodes so that when an element of the first panel is caused to emit light, a potential is applied to conductive elements in the first and second electrodes of the second panel to activate the corresponding portion of the layer and transmit light through that portion whilst preventing light from passing through other portions of the layer. Circuits are provided to operate the display panel.

2 7. I l 42 I I llf l l IHI /46 NH/3 l I 4 k :IIIIL/43 l I I 'III 5 I IIll: 6 l [I I hit 45 INVENTOK Pump c. NOREM OVN PATENTEDFEBZBM "3566314 I SHEEY S-UF 6 ZIO PULSE IN 8 AMPLIFICATION h PULSE OUT '4 IQMWZRROK Wm? c. mum.

Ram-m ELECTROLUMINESCENT DISPLAY SYSTEMS This invention relates to information display systems and to improved display screens therefor.

In radar display consoles and television display sets, high vacuum cathode ray tubes have been used extensively together with associated high potentials. Solid state circuits have been incorporated in many television receiver sets but no satisfactory substitute is known for the cathode ray tube requiring several thousand volts of potential for operation.

One proposal for a display system is replace the above-mentioned cathode ray tube and which does not utilize such high voltages is disclosed in Canadian Pat. No. 627,213 to Ford E. Williams which issued on Sept. 12th, 1961. However, the display system and display screen disclosed in that patent utilizes light amplifying cells which are made up of continuous, i.e. un broken, layers and suffered from the disadvantage that, when it was used, background illumination was present and detracted from the overall picture effect which is, of course, a disadvantage.

From one aspect of the present invention, it is an object to provide an improved display screen in which the above-mentioned disadvantage is reduced or substantially obviated.

Accordingly, there is provided a display screen comprising a first multielement component panel in which each element thereof is capable of emitting light when selectively activated, and a second component panel adapted to transmit substantially only that light from a selected element and to prevent the transmission of light from nonselected elements.

In one construction according to my invention, larrange for the second component panel to transmit substantially only that light from a selected element by constructing at least a part of the second component panel in strip form.

According to another aspect of the invention, I provide a display system including a display screen comprising a first multielement component panel including an electroluminescent layer in which each element thereof is capable of emitting light when selectively activated and a second component panel adapted to transmit substantially only that light from a selected element and to prevent the transmission of light from nonselected elements, said second component panel comprising a sandwich of materials capable of transmitting light from said first component panel on activation of a respective element thereof, said first component panel including a first set of conductors located on one side of said layer and a second set on conductors located on the opposite sides of said layer whereby a selection matrix is formed to selectively develop an electric potential across any required element of said first component panel so that light is transmitted therefrom on activation of the respective element by said potential, said second component panel comprises a glass substrate on which are etched tin oxide electrodes to constitute a first set of said conductive strips, a photoconductive layer, an opaque conductive layer, a layer of electroluminescent material, a second set of tin oxide electrodes to constitute a second set of said conductive strips, and a layer of glass, whereby the first and second sets of conductive strips are parallel and on opposite sides of said layer of electroluminescent material to permit selective activation of said strip portions of the electroluminescent material in the second component panel, circuit means associated with said second component panel to select that conductor in its respective first set and that conductor in its respective second set corresponding to the required portion of the second component panel whereby a potential may be applied thereacross to activate that portion whilst all other portions of the second component panel are retained inactive, and means for applying a potential across said portion at the instant that light is emitted from the corresponding element in the first component panel.

According to a further aspect of the invention, l provide a color image presentation system comprising a composite panel composed of a first component panel of a luminescent material which when excited to luminescence emits light radiation, a second component panel composed of a plurality of elements each of which will transmit said radiation only when simultaneously excited by the excitation of said first component panel layer and an electric field, a third component panel composed of a plurality of light amplifying elements each of which emits a'primary color emission when simultaneously excited by the emission of said first component layer and an electric field, said light amplifying elements being arranged in groups whereby an excitation of respective light amplifying elements in the same group a different primary color emission occurs.

According to yet another aspect of the invention, I provide a method of providing a visible display in response to electrical signals including the steps of providing a display screen comprising a first multielement component panel in which each element thereof is capable of emitting light when selectively activated and a second component panel adapted to transmit substantially only that light from a selected element and to prevent the transmission of light from nonselected elements, said second component panel being composed of a multielement layer having a first set of conductors on one side and a second set of conductors on the opposite side thereof whereby on application of a potential between a conductor in the first set and a conductor in the second set a respective ele ment of said layer in said second component panel is activated and if light from said first panel is .simultaneously incident thereon, then light is transmitted by said element of the second component panel, and including the steps of causing the respective elements of the first component panel to emit light incident on corresponding elements of the second component panel and simultaneously applying potential between respective conductors of said first and second sets whereby the respective element of the second component panel transmits the light incident thereon from the first component panel whilst preventing other elements of the second component panel from transmitting a light therethrough.

According to yet a further aspect of the invention, I provide a method of constructing a component panel for a display screen including the steps of coating a first sheet of glass with a transparent conductive electrode layer, then coating said first sheet with a layer of photoconductive material, utilizing an etching technique on said first sheet to form said conductive layer and photoconductive material into strips, coating a second sheet of glass with a transparent conductive electrode layer, then coating said second sheet with a layer of photoconductive material, utilizing an etching technique on said second sheet to form said conductive layer and photoconductive layer into strips, coating the strips on said first sheet with a conductive opaque glue, placing the two glass sheets together with the strips in alignment and facing each other whereby they adhere together to form said component panel comprising the first and second sheets with said strips between them.

The invention will now be described as applicable to a television system and, by way of example, with reference to the accompanying drawings in which:

FIG. 1 is a diagrammatic representation of a display screen for a black and white television receiver according to the present invention and including a first, second and third com ponent panel; a

FIG. 2 is a cross-sectional view of the first component panel of FIG. 1 taken on the line II-II of FIG. 4;

Flg. 3 is a cross-sectional view of a first component panel similar to that shown in FIG. 2 but designed for use in a color television receiver;

FIG. 4 is a frontal view of the display screen shown in FIG. 1 to illustrate the crossed grid selection matrix;

FIG. 5 illustrates a horizontal scanning control circuit for use with a display screen according to the present invention;

FIG. 6 illustrates a vertical scanning control circuit for use with a display screen according to the present invention;

FIG. 7 is a diagrammatic representation showing the connection of control circuits to a part of the display screen in a color television system;

FIG. 8 shows an additional control circuit;

FIG. 9 is a detailed crosssectional view of a display screen in accordance with the present invention for use in a color television system;

FIG. It) illustrates a modification to the display screen of FIG. 9 for a black and white television system;

FIG. 11 is a diagrammatic representation of the second component panel according to a further embodiment of the present invention;

FIG. 22 is an enlarged view of the panel shown in FIG. 11 so as to illustrate the formation of conductive strips thereon;

FIG. I3 is a cross-sectional view to illustrate the construction of the component panel of FIG. ll;

FIG. 14 shows a further horizontal scanning control circuit;

FIG. 15 shows a further vertical scanning control circuit;

FIG. 16 is a diagrammatic representation of a control circuit incorporating a clock pulse counter;

FIG. I? illustrates a further control circuit;

FIG. id shows a further control gating circuit which may be used in a color television system according to the present invention; and

FIG. 19 is a diagrammatic representation of certain pulses present in a part of the described circuits.

In FIG. I, there is shown a display screen, i.e. panel, in accordance with the present invention and it will be seen to comprise three component panels I, 2 and 3. A cross-sectional view of the first panel on line II-II of FIG. 4 is shown in FIG. 2 and the panel will be seen to consist of a glass plate 4 which is designed to support a strip panel 5 of electroluminescent material and an associated electrical grid comprising a first set 6 of tin oxide conducting strips extending in one direction, e.g. vertically, and a second set 7 of conducting strips extending at right angles to the first set, e. g. horizontally. The second set 7 of conducting strips is deposited, for example by chemical or other means, on the glass plate 4 whilst each of the conducting strips in the first set 6 is deposited on the outer surface of a respective strip of electroluminescent material 5. In this way, a selection matrix is provided so that by applying a potential between a conductive strip of the first set and a conductive strip of the second set, any particular element of the electroluminescent strip panel can be selected and activated by the potential thereacross.

It will be appreciated that when the display screen of FIG. I is used, the first set 6 of conducting strips will extend vertically and the second set 7 will extend horizontally. Each set may conveniently include 256 conductive strips. The display screen may be used alone or may be inserted in an envelope including an electron gun whereby elements of the first component panel may be activated by an electron beam instead of, or as well as, by a selection matrix.

In a television receiver, three information signals are produced which may be utilized in a display system according to the present invention. These comprise the vertical synchronizing pulses, the horizontal synchronizing pulses, and a representation of the signal amplitude at each point. A color television receiver also provided information as to the signal amplitudes of the three color signals and therefore, a display screen for a color television receiver according to the present invention will utilize the synchronizing pulses in the same way as one for a black and white television receiver but, in addition, will utilize the color signal amplitudes to produce a color ima e.

Fl G. 2 is a cross-sectional view of a first component panel 1 designed for black and white television. For color television, it is necessary to provide three parallel conducting strips, i.e. electrodes, for each of the electrodes of the first set 7 of FIG. 1 so that the normal three colour signals from the colour circuits of the television set may each be fed to a separate conducting strip.

A component panel I for color television is shown in FIG. 3 and is substantially identical to that shown in FIG. 1 except that three parallel conductive strips 8, 9 and It) (i.e. three vertical electrodes, respectively the red, green and yellow electrodes) are provided in place of each conductive strip 6 in FIG. 2. However, the total overall size of the electrodes 8, 9 and 10 will be the same as that of each vertical electrode 6. The electroluminescent layers 5 under the electrodes are similarly split as shown in FIG. 3. In use, the three parallel electrodes 8, 9 and I0 are supplied with the three different signals from the three amplified color signals derived from the conventional circuits of the color television receiver.

FIG. 4 is a plan view of the component panel I of FIG. 2 to illustrate the selection matrix. One conductive strip 11 of the first set is especially indicated as also is one conductive strip 12 of the second set of conductive strips. In this way, it can be clearly seen how selection occurs of that element of the electroluminescent layer 5 which is positioned between, and at the intersection of, the two conductive strips II and 12. The first component panel ll, when operating, generates a moving point of light as each element is activated and each point is of constant brightness. Sequential illumination of the elements causes the point of light to move across the panel.

The second component panel 2 of the display screen is a light amplifier panel which is arranged to truncate, i.e. cutoff, the light pulses from the electroluminescent layer in the first component panel i when they would blur the picture. The truncation is achieved by momentarily disconnecting the second component panel 2 and this is equivalent to a truncation pulse sweeping across the second component light amplifier panel. This disconnection, i.e. truncation pulse, is accomplished by interrupting the high voltage supply to the respective vertical strip of the light amplifier panel 2 just as the electroluminescent layer elements associated with, and adjacent, that strip are activated.

A circuit for supplying an activating voltage to an electroluminescent layer conductive strip of the first set 6 is shown in FIG. 5 and includes a circuit for interrupting the high voltage supply to the respective vertical 'strip of the second component light amplifier panel. If the electroluminescent layer is, as mentioned above, provided with 256 vertical conductive strips in the first set and similarly 256 vertical strips are provided in the light amplifier, then 256 circuits as shown in FIG. 5 will be required to scan horizontally across the television screen.

The circuit shown in FIG. 5 may be referred to as the horizontal scanning circuit and comprises a transistor 200 having associated resistors 21 and 22 and capacitor 23. A positive voltage of substantially 20 volts is applied to terminal 24 of the transistor circuit whilst a control gating voltage may be applied through capacitor 23 to the base electrode of transistor 200 by means of a gate circuit 25.

The transistor 2M) is normally cutoff and no potential is developed across resistor 21. However, as soon as the correct combination of gating inputs is applied to gate circuit 25, transistor 200 is caused to conduct and a voltage is developed across resistor 21. This voltage is applied along wire 26 to the respective vertical conductive strip of the first set 6, for example strip 11 in FIG. 4, and if a voltage is simultaneously applied to a horizontal conductive strip, such as 12 in FIG. 4, then that I element of the electroluminescent first component panel at their intersection will be activated so that a spot of light is generated-the brightness of the light spot, i.e. light pulse, is the same for each element of the electroluminescent panel. The other elements of the electroluminescent panel I which are under the strips II and I2 are actually half-selected and, therefore, an unwanted background illumination may be emitted by those strip elements which are not actually selected since they are not at the intersection of strips 11 and 12, The way in which at least part of this unwanted background illumination may be reduced is as follows.

At the same time as a voltage is applied along wire 26, a truncating voltage is also applied along wire 27 to the electrode 28 of transistor 2% which is normally cutoff. Transistor 29 thus conducts and the voltage on line 27 is applied through a diode 31 to a particular vertical strip of the second component light amplifier panel 2 (FIG. Ii). That particular vertical strip is the strip corresponding to that strip of the first com ponent panel which has just been deactivated. Therefore, for example, wire 26 in FIG. 5 may be connected to the 12th strip then the output of diode 31 will be applied to the 11th strip. Therefore, unwanted background illumination from unselected elements, especiallythe immediately preceding activated elements, of the electroluminescent panel is reduced to a minimum. The light from the selected element of the electroluminescent panel is, therefore, passed without interference. In this way, a better and more acceptable display can be obtained, for example in a television receiver.

A vertical scanning circuit for selecting the horizontal conductive strips of the electroluminescent first component panel 1 (i.e. the conductive strips of the second set 7 in FIG. 4) is shown in FIG. 6 which consists of a transistor 32 which is supplied with a negative voltage of substantially 60 volts at terminal 33. A control gating input may be applied to the base of transistor 32 from a gate 34 through a resistor-capacitor network 35. When transistor 32 is caused to conduct, the resulting voltage developed across resistor 36 is applied to a horizontal conductive strip, such as 12, of the second set 7 via lead 37 in FIG. 6 and vertical scan lead 47 in FIGS. 1 and 4. If the second set 7 includes 256 horizontal conductive strips, then 256 vertical scanning circuits, as in FIG. 5, will be provided so that selection of any element of the electroluminesccnt panel 1 may be made by means of the logic gating circuits.

In order to build up a complete picture frame, the elements of the electroluminescent panel are activated in sequence so that a moving point of light appears to pass over the panel to form a picture roster-the shape of the raster will, of course,

be determined by the controlling circuits in a well known manner.

The light pulses which pass through the second component panel then pass through the third component panel. An optical filter may be interposed between the second and third component panels or between the first and second component panels to reduce light from the decay tail of the electroluminescent material whereby only photons corresponding to electric dipole transitions (the first portion of the pulse) are allowed to pass.

The third component panel 3 (FIG. 1) is a light amplifier, capable of operating at least at frequencies above mc./sec., which is so designed that by varying its amplification as various segments of the panel are illuminated, a coherent picture display is produced. For a black and white television display, this panel may be of one-piece construction with, preferably, five layers of material. Referring to FIG. 1, these layers will be a transparent electrode layer 40, a photoconductive material layer 41, an opaque conductive layer 46, an electroluminescent material layer 42, and a second transparent electrode layer 43. In use, a voltage signal of about 150 volts positive is applied between the two transparent electrodes 40 and 43 by way of wires 44 and 65. This voltage signal is amplitudemodulated in accordance with the signal strength of the television signal. It will be appreciated that in some arrangements, the opaque conductive layer 46 maybe omitted.

In the case of a color television receiver, the third component panel 3 is divided into numerous vertical strips of four layer amplifiers. These vertical strips are in groups of three corresponding to the three primary colors of the spectrum so that activation by light from the electroluminescent panel 1 causes the selected vertical strip of a selected group to emit the required primary color.

The circuits required for the display panel are naturally more complicated since a selection must also be achieved between the three vertical color strips in each group and, for this purpose, three appropriate signal connections must be provided for each group. By feeding these three signals directly to each panel, I believe that an unnecessarily large electrical load would be placed on the system and would prevent it working. Therefore, according to my invention, those vertical color strips which produce red light are connected to the modulated 20 mcJsec. signal corresponding to the red portion of the picture. Since this group of vertical colour strips only contains between 5 to 10 strips too great a load is not placed on the rest of the circuit.

Similar circuit connections are, of course, made for those groups of vertical color strips which correspond to the green and yellow primary colors of the television picture. In this way, the appropriate signals can be supplied to the color strips of the third component panel 3 to provide the required color television picture.

The logic circuits for determining which of the third component panel's vertical strips are supplied with an activating voltage at any time may be similar to the circuits for vertical and horizontal scanning of the electroluminescent panel 1 but may be much simpler since only 10 to 20 circuits may be required.

FIG. 7 is a diagrammatic representation of the third component light amplifier panel 3 showing the way in which the three signals may be applied to the panel to select either the red, green or yellow-producing vertical color strips of the light amplifier panel 3. The vertical color strips of the panel are actually divided up into several main groups and, for con venience, one such group 50, e.g. including I0 to 20 strips, is shown in FIG. 7.

All the vertical color strips capable of producing a red light are connected to a lead 51, all the vertical color strips capable of producing a green light are connected to a lead 52 and all the vertical color strips in the main group 50 capable of producing a yellow light are connected to a lead 53. Leads 51, 52 and 53 are connected to the secondary windings 54, 55 and 56 of transformers 57, 58 and 59. Therefore, when a gated input pulse is applied to one of the primary input terminals 60, 61 or 62, then the respective red, green or yellow color strips are activated to produce the corresponding color on the television screen. In this way, the color television picture is formed.

In FIG. 8, an alternative logic circuit is shown comprising a transistor 63, whose base electrode may be supplied with a gated control signal along lead 64 from a gating circuit 65 having a plurality of inputs 66, at least some of which are provided with clock pulses from the central control clock pulse generator for the display system. An input color signal modulating the 20 mc./sec. carrier is applied to transistor 63 along lead 67. Thus, when transistor 63 conducts, an output voltage may be obtained across resistor 68 and fed through capacitor 69 to output terminal 70.

In FIG. 9, there is shown the detailed construction of a display screen according to the present invention for use in a color television set. The same reference numerals have been used in FIG. 9 as have been used in FIG. 1 and, therefore, the first component panel I is shown as being made up of vertically extending electrodes 6 which-are, in use, connected to the horizontal scanning circuits (i.e. the first set 6 of conductive strips referred to above), a layer 5 of electroluminescent material (for example, Zn S) and finally, the horizontally extending transparent electrodes 7 which are in the form of tin oxide (SnO) formed on a glass plate --these comprise the second set 7 of conductive strips referred to above and are, in use, connected to the vertical scanning circuits.

The second component panel 2 consists of a plane trans- I parent electrode layer 80 made up of a plurality of conductive strips, an unbroken layer 81 of photoconductive material either in strip form or continuous, a, preferably, continuous opaque conductive layer 79, a layer 82 of electroluminescent material, and a segmented (i.e. strip form) electrode layer 83. The electroluminescent layer 82 may, for example, be a segmented zinc sulfide (Zn S) layer and preferably, the opaque conductive layer 79 should conduct only in the vertical direction although it will be appreciated that a layer which conducts equally in all directions would also be suitable and probably more readily available.

The third component panel 3 consists of a plane transparent continuous electrode layer 84, a continuous, unbroken layer 85 of photoconductive material, an opaque, conductive layer 86, an electroluminescent segmented layer 87 of zinc sulfide material (Zn S), and a segmented electrode layer 88. The third component panel 3 is, therefore, similar to the second component panel 2--the zinc sulfide layer 87 is, however, much more timely segmented and each strip is doped with impurities which result in the production of different colors from adjacent strips. Alternatively, adjacent strips may stimulate phosphorescent elements which, in turn, provide the required colors.

For a black and white television receiver, the construction of the display screen is similar to that shown in FIG. 9 but the third component panel 3 is as shown in FIG. 10 and is identical in composition and design to the second component panel 2 of FIG. 9 except that the electroluminescent layer 87A and the electrode layer 88A are unbroken.

In a second embodiment according to the present invention, it is proposed that a different orientation of the scanning shutter, i.e. component panel 2 of FIG. 1, should be used. Instead of using a constant intensity scan with variable light amplification in the third stage, i.e. component panel 3 of FIG. I, a variable intensity scan with a constant third stage of light amplification is used. For this purpose, the second component panel 2 of the display screen is constructed as a sandwich light amplifier whose function is to suppress light produced by the half-selected areas of the electroluminescent layer and to provide some amplification for the light produced by the fully selected element of the electroluminescent layer. To achieve this, the second component panel 2 is provided with diagonal, electrically independent strips running from the lower left portions of the panel to the upper right portions as shown in FIG. 1 l. The photoconductive strips each comprise a series of substantially square-shaped areas, said areas being each connected to adjacent areas in the same conductive strip at diagonally opposite corners as shown in FIG. 12. Those strips which terminate on the right side of the panel are connected by wiresto other strips starting on the left hand side of the panel at substantially the same height. For example, conductive strip 98 is connected to conductive strip 91 by means of wire 92. Nonconductive gaps, such as 93 and 94, are provided between the conductive strips and the arrangement and shape of the conductive strips is such as to ensure uniform amplification over each square of electroluminescent element. 95 indicates a portion corresponding to FIG. 12.

In FIG. 12, there is shown an enlarged view of a portion of the panel of FIG. 11 and it will be seen that the conductive strips such as 91 are not absolutely straight but are provided with a wave-shape.

In FIG. 13, a cross section through the second component panel of FIG. 11 is shown. The panel consists of a glass substrate 96 on which are etched tin oxide electrodes 97. The panel also includes a photoconductive layer 93, an opaque layer 99, a layer of electroluminescent material lllll, tin oxide electrodes i911 and a layer of glass 102.

In FIG. 11, the external wires connecting the conductive strips of the second component panel to external circuits are identified as 104. The wires We are actually shown opposite gaps between conductive strips but are, of course, each connected to a conductive strip, for example that one horizontally to the left in FIG. 13. Suitable AND circuits and clock circuits are connected to the wires lll l so as to control the operation of the second component panel 2 in the required manner. It is arranged that the conductive strips thereof are turned on one at a time only and in such a way that that strip which is on at any time crosses directly over the fully selected element of the electroluminescent layer 5 in component panel I of FIG. 1. Thus, the light emitted by that electroluminescent layer is amplified whilst the unwanted illumination from the half-selected elements of that electroluminescent layer are, in contrast, opposite inactivated portions of the light amplifier second component panel 2 and thus, any light produced by them is prevented from passing through to succeeding portions of the display screen and thus the unwanted background illumination is reduced or substantially obviated.

A useful feature of the second component panel according to the second embodiment of the present invention and as shown in FIG. ii, is that the same type of construction can be used no matter the second component panel is intended to be used in a display screen for color television or for black and white television. Similarly, if a display screen intended for black and white television is converted for operation in a color television system, then the second component panel as illustrated in FIG. 11 will not require any alteration.

The electrical connections to the second component panel are similar to the electrical connections to the electroluminescent layer in the first component panel I as described below. Circuits substantially identical to the clock circuits used for the horizontal scanning may be used to switch a 20 mc./sec., 200 volts oscillation from strip to strip, e.g. from strip to 93, etc. in FIG. ll. However, instead of being reset to zero at each synchronization pulse, another square wave pulse is sent to the counter. This ensures that the particular strip which is receiving voltage will always pass over a fully selected electroluminescent element. Resetting to zero takes place only with the occurrence of a vertical scan synchronization pulse.

For convenience, alternative circuits for use with the first component panel 1 of FIG. 1 will now be described.

In FIG. 14, there is shown a horizontal scanning circuit. 256 of these circuits may be requiredfor a television receiver system and will be each connected to a different one of the first set 6 of conductive strips shown in FIG. 4. Similarly, FIG. 15 is a representation of a vertical scanning circuit and, for a television receiver, 256 of these circuits may well be required, each for connection to a different one of the second set 7 of conductive strips in the first component panel illustrated in FIGS. 1 and 4.

The horizontal scanning circuit illustrated in FIG. 14 comprises semiconductive diodes llll, 111 and 112 connected between respective terminals 113, 114, 115 and a common line 116 to which is connected an output terminal 117 and one end of a resistor 118. The other end of resistor 118 is connected to a terminal 319. In use, the terminal 113 is the signal input terminal for the scanning circuit, terminals 114 and 115 are connected to a clock pulse counter generator which is shown in FIG. 16. Terminal 119 is connected to a positive voltage supply and in this way, the horizontal scanning circuit operates substantially as a gate circuit and supplies an output to the respective conductive strip in the first component panel 1 via terminal 117 when the correct combination of input voltages is present at terminals 113, IM and 115.

The vertical scanning circuit illustrated in FIG. I5 is similar to the circuit illustrated in FIG. M except that the diodes are reversed and a negative voltage source is used. Semiconductive diodes 120, 121i and 122 are connected between respec' tive terminals 123, 124, I25 and a common line 126. An output terminal 127 is connected to line 126 as also is one end of a resistor I28 whose other end is connected to a terminal 129.

Terminal 123 is the signal input terminal for the vertical scanning circuit, terminals 124 and 125 are connected to a clock pulse counter circuit similar to the one indicated in FIG. 16 except that it is designed to .operate with opposite polarities. Output terminal 127 is connected to the respective conductive strip either directly or indirectly whilst terminal 129 is connected to a negative voltage source whereby the vertical scanning circuit operates substantially as a gate circuit in a manner which is well known in the art.

In FIG. 16, there is shown a circuit for producing clock pulses for supply to the terminals 114 and 115 of the horizontal scanning circuit shown in FIG. M. A similar circuit will, of course, be provided for supplying the clock pulses to terminals 124 and 125 of the vertical scanning circuit shown in FIG. l5. In FIG iii, an electronic counter l3ll is controlled by a square wave input, referred to previously, on line 131 so as to provide timing pulses on a first set of four leads I32, I33, 134 and 135. These timed pulses are eventually effective to control the supply of the required clock pulses to the respective terminals 114 of FIG. 14. Counter 130 also supplies a series of timed pulses on a second set of four leads 136, 137, 138 and 139. These pulses are eventually effective to supply the required clock pulses to each of the terminals 115 of all the 256 horizontal scanning circuits.

The leads 132, 133, 134 and 135 are all connected to the respective inputs of 16 control circuits such as that identified as 140 in FIG. 16. Circuit 140 includes a four input gating circuit 141 which is adapted to receive an input from each of the lines 132, 133, 134 and 135. The output of gating circuit 141 is fed along line 142 to the base electrode of a transistor 143 whose circuit incorporates a resistor 144 connected to a positive voltage supply via terminal 145. An output is taken along lead 146 which eventually connects to 16 individual leads, identified generally as 147, which are each connected to a terminal 114 in a different one of the horizontal scanning circuits such as shown in FIG. 14.

Since each of the 16 circuits 140 includes 16 output leads 147, there are thus 256 output leads 147, i.e. one for each of the 256 horizontal circuits of FIG. 14.

To obtain the necessary pulses for application to the terminals 115 in the 256 horizontal scanning circuits, 16 composite circuits 150 (FIG. 16) are provided. These are similar to the circuits 140 and each of the leads 136, 137, 138 and 139 are connected to the inputs of all the respective gating circuits 151 in each circuit 150. The output of the gating circuit 151 is connected along lead 152 to the base electrode of a transistor 153 whose circuit incorporates a resistor 154 connected to a terminal 155 which is supplied with a positive voltage. An output is obtained along lead 156 which is connected to 16 output leads identified generally as 157. Each of the output leads 157 is connected to a terminal 115 of a different one of the horizontal scanning circuits. Thus, since there are 16 leads 157 and sixteen composite circuits 150, there is thus provided a sufficient number of output leads 157 to supply the required pulses to all the terminals 115 in the 256 horizontal scanning circuits.

As mentioned above, circuits similar to FIG. 16 are provided for the 25 6 vertical scanning circuits of FIG. 15.

The circuits which are provided for providing voltage inputs to all the terminals 113 (FIG. 14) of the 256 horizontal scanning circuits and to terminals 123 (FIG. of the 256 vertical scanning circuits are determined by an Equation I below.

As will be understood, the final output amplifying stage of conventional electronic circuitry is usually linear. That is to say, V out a V in, where a is a numerical constant expressing the average amplification of the circuit. In the abovedescribed embodiments of the present invention, it is desirable to ensure that:

so that the nonlinear effect of the electroluminescent panel can be compensated. B is used as a numerical constant in the equation with a value (measured in volts) dependent on the specific electroluminescent material used.

Having regard to Equation 1, the input signals for terminals 113 and 123 may be provided by a circuit as shown in FIG. 17 which provides an approximation to the ideal circuit required to satisfy Equation 1.

Referring to FIG. 17, the circuit consists of a transformer 160 whose primary winding 161 is connected via terminals 162 and 163 to the output from an output amplifying stage (not shown). The secondary winding 164 of transformer 160 is center-tapped with the center tap being connected to earth, i.e. ground, potential. Opposite outer ends of the secondary winding 164 are connected to terminals 165 and 166. A positive voltage is supplied to terminal 165 through resistor 167 whilst a negative voltage is applied to terminal 166 through resistor 168. A first output from the transformer is taken from terminal 165 through lead 169 to terminal 113 of FIG. 14,

whilst a second output is taken from terminal 166 through lead 170 to terminal 123 of FIG. 15.

To provide the necessary clock pulses for the horizontal and vertical scanning of the display screen, electronic counters are used comprising eight or nine bistable digital flip-flop circuits which are interconnected in a well known manner. The input to these counters is provided by one astable flip-flop circuit for the vertical scanning circuits and one astable flip-flop circuit for the horizontal scanning circuits. Timing pulses are thus set to the vertical scan clock circuit every 70 microseconds, and to the horizontal scan clock circuit every one half to one quarter microsecond. The counting circuits themselves are, as mentioned above, of the type well known in the art and are initialized at zero, i.e. reset to zero, by the synchronization pulses referred to above.

The third component panel 3 could well be a simple light amplifier designed to brighten the image produced by the first two component panels 1 and 2 of FIG. 1. The light amplifier component panel 3 may well be similar to the second component panel 2 except that both tin oxide electrode layers are solid and cover the entire area of the panel without gaps. As will be clear from the above, and with reference to FIG. 1, the construction of the third component panel will be first a transparent conducting electrode layer 40, then a photoconductive layer 41, an opaque conductive layer 46, followed by an electroluminescent layer 42 covered by another plane electrode layer 43 of transparent material. The voltage applied between the two electrode layers 40 and 43 should preferably be an alternating voltage of about 150 or 200 volts at a frequency of 20 mc./sec. However, it will be appreciated that the most desireable voltage and frequency may well be determined by experiment.

It will be appreciated that in some arrangements, the opaque conductive layer 46 may be omitted. Furthermore, the second component panel may comprise a glass substrate on which are etched tin oxide electrodes to constitute a first set of said conductive strips, a photoconductive layer, an opaque conductive layer, a layer of electroluminescent material, a second set of tin oxide electrodes to constitute a second set of said conductive strips, and a layer of glass, whereby the first and second sets of conductive strips are parallel and on opposite sides of said layer of electroluminescent material to permit selective activation of said strip portions of the electroluminescent material in the second component panel.

When the display screen is constructed for color television, the third light amplifier panel will be slightly modified in that its electroluminescent layer 42 will be divided into vertical strips of electroluminescent material corresponding to the division in FIG. 3 for the first component panel 1. The vertical strips of electroluminescent material in component panel 3 will each radiate that color of the electroluminescent material they are intended to amplify.

Some additional information will now be given as to the circuits which could be used to operate the display screen illustrated in FIGS. 9 and 10. It is to be appreciated that this information may be considered as an elaboration of the information given above but that, in certain instances, it will preferably be applicable to an alternative embodiment as will be clear from the description below.

The circuits illustrated in FIGS. 14 to 17 are advantageous in that their cost is relatively low, their design is relatively simple and the resultant arrangement is of relatively small size when compared with vacuum tube circuits. Clock pulses from the clock counter circuitry will be applicable, in a well known manner, to layers 7 and 6 of component panel 1 (FIGS. 9 and 10), and to layers 83 and of component panels 2 and 3 respectively. For layers 7 and 6 of component panel 1, there is no necessity to provide a corresponding terminal 113 of FIG. 14, but a terminal 113 will be provided in respect of layer 83. The voltage applied to that terminal 113 will be the variable amplification potential having a DC bias whereby it will vary between ground potential and 200 to 300 volts.

When the display screen of FIG. 9 is constructed for use in a color television set, it is desirable that a more sophisticated diode network be used in respect of layer 88 of component panel 3. Such a diode network is shown in FIG. 18.

Referring to H6. E8, the diode network comprises a first gating circuit having diodes Mid and mi supplied with the required voltage pulses via terminals llldA and 115A respectively-these terminals corresponding to terminals lid and H of HG. M. in a well known manner the diodes lhtl and llfill are connected to a common line 182 which is connected to ground potential through resistor res. A common lead 134 is taken from lead 1182 and one diode of each of a plurality of subsidiary diode and gating circuits is connected to lead Edd. The first subsidiary diode and gating circuit includes diodes Edd and res, diode W5 being supplied with a gating voltage from the common line w ll and diode ldti being supplied with its respective gating voltage by way of a terminal 187, which, in use, is supplied with the respective red" signal from the color circuitry of the television receiver. As shown, the diodes 185 and E86 are connected to a common point 11% which is connected to ground potential through a resistor m9 and is also connected to output terminal 1%. In use, terminal 1% is connected to a red" strip of the electroluminescent (SnO) layer of the component panel 1, i.e. to the red conductive strip electrode d of FIG. 3in practice, it may be connected to several such strips 8.

For the green signals in a color television receiver, a similar subsidiary gate circuit is provided consisting of diodes 191 and 11% associated with terminal 193, resistor I94 and terminal lhE-diode W1 is, of course, also connected to comthen lead 1%. The green signals from the circuits of the television receiver are supplied to terminal 193 and the output from terminal W5 is supplied to the conductive strip electrodes made of electroluminescent material (SnO) material associated with the color green in the television display, i.e. electrodes 9 in FIG. 3.

A subsidiary gating circuit is similarly provided for the yellow signals of the color television receiver and this comprises diodes 11% and E97. Diode 1% is connected to the common lead lhd whilst diode i9? is supplied with the appropriate yellow" television signals through terminal 1%. The opposite terminals of the diodes 1% and I97 are connected to ground through a common resistor 19? and the output from this subsidiary gate is fed, through terminal 210 to the respective conductive electrode strip or strips (FIG. 3) associated with strips of electroluminescent material (SnO) designed to produce yellow light on activation.

Whilst in the above description, the color television receiver has been referred to as supplying red" signals, green signals and yellow signals, it is to be appreciated that the receiver might well supply red signals, green" signals, and "blue signals or any combination of color signals, or number thereof as required in the design of the television receiver or other display apparatus.

It is also to be appreciated that the OR gates of the clock circuits for layer d8 may be replaced by'AND gate circuits as required. 1

With the additional information given above and from a consideration of the figures, the operation of the display screens according to the present invention and the associated circuits will be understood. As mentioned above, a signal is produced in the first component panel 1 which is of constant amplitude. This is truncated and modulated in the second component panel 2 and in a black and white television system, the signal is then amplified in component panel 3a of H6. 10. For a color television system, the signal from the second component panel is amplified separately for the three colors in the third component panel 3, a different amplification ratio normally being necessary for each color.

it should be mentioned here that the second component panel would appear to utilize spatial integration of the time signals which is achieved by selective amplification. FlG. ill! is a graphical representation as to how this is achieved. The first,

upper, graph therein represents the input pulse plotted against time, whilst the second, middle, graph is a representation of the amplification which is provided. In the third, lower graph, the output pulse is shown.

It will be appreciated, from the above, that differentiation of the averaged color signals is a preferable method of accentuating the variation and contrast of the picture when the differentiated signal is applied to the strips of layer 83 in FIG. Q. However, this may be investigated quite simply by experiment.

From the above description, it will be seen that the problem of unwanted light which was found to be present in a display screen constructed in accordance with Canadian Pat. No. 627,213 is reduced or substantially obviated in a display screen in accordance with the described embodiments of the present invention and the resulting image is, therefore, clearer. As will be clear from the above, the unwanted background illumination in the prior art display screen referred to was due to light being produced by electroluminescence which had only been half-selected. This light was, of course, much fainter than that produced by the fully selected electroluminescent element but there are usualiy one to two thousand half-selected elements and only one fully selected element. Thus, it will be evident that the half-selected elements may well combine to produce as much as ten times the light from a fully selected element. It is believed that efforts have been made in the past to reduce this undesirable result by providing a nonlinear resistivity layer. However, such a layer must work extremely well for the total suppression of the unwanted light to be satisfactory and this is difficult to achieve. Furthermore, such a layer is difficult to fabricate.

As mentioned above, the display screen according to the present invention which is shown in FIG. ll includes a second component panel 2 which is so constructed that its amplification is selective and some of the horizontal halfselected elements are suppressed by simply not amplifying the light produced by the respective electroluminescent elements. The conductive strips of the second component panel are, as shown, arranged at 45 across the panel and instead of all of the strips but one being on at any given time, it is arranged that all of them are off except one. This conductive strip is activated and selected by the electronic circuitry in such a way that it is that strip which crosses over the fully selected electroluminescent at the instant when it is activated. Owing to the 45 tilt, it does not cross over any half-selected elements at all and so only the fully selected electroluminescent element of the component panel 1 has its light amplified, the half-selected elements being rendered ineffective by the nonoperative portions of the amplifier.

As mentioned above, the second component panel 2 (FIG. l) is a light amplifier in composition but it functions as a light suppressor. In fact, it would be satisfactory if that panel provided no amplification whatsoever but only suppressed the various forms of unwanted light. With this in mind, the panel is divided physically in the manner described above. Each section is activated only when it is required to amplify (or only transmit) a true light signal as opposed to the various types of noise encountered in display screens.

It will be apparent that the second component panel may be activated by means of vertical conductive strips only so as to activate strips of the panel or by means of vertical and horizontal strips in the form of a selection matrix to active respective elements to pass the beam of light from the first component panel.

A second source of unwanted light noise is due to the phosphorescent tail of the electroluminescent material. As will be appreciated, two different components of this phosphorescence are known although there may be others. The first is blue phosphorescence while the second component is green phosphorescence. Both these components are generally undesirable because the light they make is not produced at the same instant in time at which they are activated electrically but is produced at a later time which may be from 5 microseconds to l millisecond. By this time, the

final color amplifier has been readjusted to amplify light from another portion of the picture, this new amplification having a different amplification factor. The unwanted light components having a blue or green phosphorescence would also be amplified by this factor but this would only produce a blurring effect on the wanted picture. This blurring would be most effective since it is possible for more than 95 percent of the light to be either delayed blue or green phosphorescence so that the picture seen on the display screen becomes 95 percent unwanted blur and only percent wanted picture signal. Furthermore, this blurring is additional to the blurring resulting from the above-mentioned half-selected elements.

A display screen according to the described embodiments of the present invention overcomes the effect of the abovernentioned two phosphorescent tails in two ways. The green phosphorescence is the worst of the two unwanted components because it is produced up to one-thousandth of a second later than the electrical pulse which produced it. However, this unwanted component is also the easiest to eliminate by merely providing a blue filter to remove it from the optical system-see the blue filters 89 and 90 in FIG. 9. The unwanted blue light component of phosphorescence is much more compact (the average delay is often as much as 3 microseconds) but it is still too slow'for a good picture. Its effect is obviated by switching the light amplifier strip off, i.e. not activating the second component'panel 2, after the arrival of the first half microsecond of the blue pulse. [t has been stated that the amplification of the strips in the second component panel 2 should be kept constant. However, in some instances, it may be desirable to vary the amplification of these strips in the second component panel as well as varying the amplification of the third component panel 3 so as not to lose any of the definition obtained-since the display screen and the circuits are designed to provide the best possible definition, every effort should be made to retain it. The precise manner in which the amplification is varied is not critical but two methods are readily apparent. The first method of varying the amplification is to make the variation the average of the three color signals whilst the second method is to make the variation the differential of that average of the three color signals. At first sight, it would seem that the second method is preferable.

It will also be appreciated that stray light may well interfere with the operation of a display screen constructed in accordance with Canadian Pat. No. 627,213 as it would appear that the three amplifier panels referred to in that patent can and will interact with each other. More specifically, the light produced by the red panel amplifier in that patent illuminates the green light amplifier in addition to the light emanating from the electroluminescent panel. If the light from the red panel is bright, then the green light amplifier will also be caused to be bright, or alternatively, if the red light is dim, then the green light amplifier might also be reduced in its illumination. This sort of feedback within the display screen may well produce effects which are difficult to describe but it is to be appreciated that all these effects are not necessarily bad. However, they may well be unpredictable and, therefore, undesirable. To overcome them in the described embodiments of the present invention, the parts of the panels are separated into strips and the strips are placed in vertical rows across the face of the third component panel three at a time as indicated above. By using light amplifier panels with opaque layers, the last trace of interference between the various color amplifying strips may well be eliminated.

The component panel illustrated in FIG. 11 may be considered as a scanning shutter light amplifier but even with this amplifier, there may still be some loss in picture contrast due to the length of the decay period for the shutter light amplifier (i.e. after it has been switched off). This could result in some sort of horizontal averaging, or spatial integration-reference should be made to FIG. 19 on this point. Once measurements have been made experimentally on a prototype screen and the parameters of this type of distortion determined, electronic circuits can be constructed to perform an inverse operation on the light amplitude control signal which would, therefore, cancel the distortion. Such a circuit for performing the inverse operation could be incorporated into the display system if the distortion is noticeable. It is to be appreciated that this modification would only effect the picture amplitude control signal and the circuit would perform a form of differentiation with espect to time in order to compensate for the horizontal spatial integration. The construction of the required circuits should present no difiiculty once the exact form of the horizontal averaging has been measured.

As mentioned above, the electroluminescent panel may be a zinc sulfide panel, the first light amplifier, i.e. the first component panel 1, may be a sandwich of zinc sulfide (Zn S) and cadmium selenide. The second light amplifier, i. e. component panel 3, may contain a cadmium selenide layer with vertical strips of zinc sulfide (Zn S) which has been doped with impurities so that the strips radiate the required respective colors when energized, i.e. activated. This type of third component panel 3 is, of course, only required for a color television receiver system and not for a black and white television receiver system wherein the second and third component panels may well be similar or even identical. The third component panel basically is a light amplifier added to increase the brightness of the image to acceptable brilliance and, in the case of a color television receiver system, to convert the black and white image produced by the first two stages into its color equivalent.

It will thus be seen that two solid state" image display panels or screens have been described wherein each is composed of three components, and the difference between them is in the manner in which the image is created. The three components are very similar between the two systems and, for the black and white versions of each, are interchangeable. In the first system, the image is produced by the first component, and electroluminescent screen with crossed electrodes, and the second component, a segmented light amplifier, cleans up the image by removing the effect of half-selected electroluminescent elements. In the second system, the electroluminescent panel generates a moving spot of light which is then amplified by the segmented amplifier in a time varying manner so that an image is produced. The segmented amplifier also acts to clean up the effect of half-selected elements in the electroluminescent layer, though this task is less important in the second configuration. The third component of each system is a light amplifier added to increase the brightness of the image to acceptable brilliance and, in the case of color, to convert the black and white image produced by the first two stages into its color equivalent.

Both of these panels should be capable of producing well defined images free of distorting effects from either the electroluminescent or photoconductive material response times. The first system gives promise of greater intensity for the same input energy. The final device may well be a combination of both approaches.

In the first panel, all three colors receive equal amplification whilst in the second, the amplification of each color is different.

As has been explained, a solid stage image display panel according to a described embodiment of the present invention employs a segmented light amplifier selectively energized as a defining filter. Optical filters are used to selectively absorb all but the light produced most quickly by electrical stimulation of the electroluminescent material. The adaption of the two stage logic decoder circuit permits switching a variable voltage to any vertical or horizontal electrode in the system.

An image of graduated intensity is generated by using the described segmented light amplifier to suppress light from half-selected elements of the electroluminescent panel even when the voltage used to stimulate the panel is variable. Some prior art methods have relied on giving the electroluminescent a cutoff voltage greater than half the maximum to be expected, below which the panel will produce no light. These methods have essentially prohibited the use of variable stimulation voltages to generate graded intensity electroluminescent images.

A known type of display screen is described in Canadian Pat. No. 627,213 and the examples of materials and construction given therein may, where suitable, be used in a display screen constructed according to the embodiments of the present invention described above.

One method which could be used to construct the second and third component panels in a display screen according to the embodiments described above is to coat a sheet of glass with a transparent conductive electrode layer, then with a layer of photoconductive material, then etch out strips of said photoconductive material and conductive electrode, then take another sheet of glass and coat it also with a transparent conductive electrode layer and an electroluminescent layer and using an etching technique to form strips of electroluminescent material and conductive electrode. Finally, take one of the two glass sheets, having the respective strips, and place a conductive, opaque glue on said strips of material, then place the two glass plates and their strips in physical contact so that they adhere together with the strips in alignment on facing each other between the glass sheets.

The described embodiments of the display system using the display screen alone without an envelope have certain advantages over known electron beam devices. It has a variety of applications. The display screen can be constructed to be relatively light in weight, of reduced size and requiring no high voltage power supply and could conveniently be used for portable television receivers. The display being essentially digital would lend itself directly to computer display problems. in one preferred arrangement, the elimination of the need for a continuously deflected electron beam makes this system useable for realizing the arbitrary random and pseudorandom scanning patterns which have been shown to reduce the amount of information needed to generate an acceptable continuous picture.

The present invention has been described in some detail with reference to a number of particular embodiments. However, it will be understood that the invention is not limited thereto but the scope of the invention is defined by the claims.

i claim:

l. A display screen comprising a first multielement component panel in which each element thereof is capable of emitting light when selectively activated, and a second component panel adapted to transmit substantially only that light from a selected element and to prevent the transmission of light from non-selected elements, said second component panel comprising a transparent electrode layer consisting of a plurality of conductive strips, a layer comprising a plurality of associated strips of photoconductive material, each extending substantially right across the respective surface of the second component panel, an opaque conductive layer, a layer of electroluminescent material, and a segmented electrode layer.

2. A display screen according to claim 1 wherein the first component panel comprises an electroluminescent layer, a first set of conductors on one surface of said layer, a second set of conductors on the opposite surface of said layer, said first and second set forming a selection matrix to permit activation of preselected elements of said electroluminescent material.

3. A display screen according to claim 1 including an optical filter positioned on one side of said first component panel to remove a predetermined portion of said light.

4. A display screen according to claim 1 including a third component panel composed of a plurality of light amplifying elements each of which is capable of emitting light when simultaneously excited by light from the respective one of said elected element in said second component panel and an electric field.

5. A display screen according to claim 3 wherein the third component panel comprises a layer of photoconductive material, an opaque conductive layer, an unbroken layer of electroluminescent material, and an unbroken electrode layer.

6. A display screen according to claim 4 wherein the second component panel is a sandwich light amplifier for amplifying light produced by a fully selected element of the first component panel, said second component panel having a plurality of diagonally extending, electrically conductive strips passing across the face of the panel whereby, in use, only the light from a selected element in the first component panel is transmitted by the second component panel,

7 A display screen according to claim 6 wherein said conductive strips each comprise a series of substantially square shaped areas, said areas being each connected to adjacent areas in the same conductive strip at diagonally opposite corners.

8. A display screen according to claim 6 wherein the second component panel comprises a glass substrate on which are etched tin oxide electrodes to constitute a first set of said conductive strips, a photoconductive layer, an opaque conductive layer, a layer of electroluminescent material, a second set of tin oxide electrodes to constitute a second set of said conductive strips, and a layer of glass, whereby the first and second sets of conductive strips are parallel and on opposite sides of said layer of electroluminescent material to permit selective activation of said strip portions of the electroluminescent material in the second component panel.

9. A display screen according to claim ll wherein said electroluminescent layer is a segmented zinc sulfide layer.

10. A display screen according to claim l wherein said opaque conductive layer is adapted to conduct in one direction only.

ll. A display screen for producing a color image comprising a first multielement componentpanel in which each element thereof is capable of emitting light when selectively activated, a second component panel adapted to transmit substantially only that light from a selected element and to prevent the transmission of light from nonselected elements, said second component panel comprising a transparent electrode layer consisting of a plurality of conductive strips, a layer comprising a plurality of associated strips of photoconductive material, an opaque conductive layer, a layer of electroluminescent material, and a segmented electrode layer, and a third component panel comprising a transparent continuous electrode layer, a layer of strips of photoconductive material, an opaque conductive layer, an electroluminescent layer segmented into strips, and a segmented electrode layer, adjacent strips of said electroluminescent layer being capable of producing different colors on excitation whereby a composite color image may be produced by the display screen.

112. A display screen according to claim ll wherein the strips of electroluminescent material in the electroluminescent layer are strips of Zinc sulfide doped with impurities whereby adjacent strips produce said different colors.

13. A display screen according to claim lli wherein the strips of electroluminescent material in the electroluminescent layer are strips of zinc sulfide doped with impurities whereby adjacent strips stimulate phosphorescent elements which, in turn, provide the required colors.

14. A display system including a display screen comprising a first multielement component panel including an electroluminescent layer in which each element thereof is capable of emitting light when selectively activated and a second component panel adapted to transmit substantially only that light from a selected element and to prevent the transmission of light from nonselected elements, said second component panel comprising a sandwich of materials capable of transmitting light from said first component panel on activation of a respective element thereof, said first component panel including a first set of conductors located on one side of said layer and a second set of conductors located on the opposite sides of said layer whereby a selection matrix is formed to selectively develop an electric potential across any required element of said first component panel so that light is transmitted therefrom on activation of the respective element by said potential, said second component panel comprises a glws substrate on which are etched tin oxide electrodes to constitute a set and that conductor in its respective second set corresponding to the required portion of the second component panel whereby a potential may be applied thereacross to activate that portion whilst all other portions of the second component panel are retained inactive and means for applying a potential across said portion at the instant that light is emitted from the corresponding element in the first component panel.

15. A system according to claim 14 wherein said circuits include semiconductor gating circuits;

16. A color image presentation system comprising a composite panel composed of a first component panel of a luminescent material which when excited to luminescence emits light radiation, a second component panel composed of a plurality of elements each of which will transmit said radiation only when simultaneously excited by the excitation of said first component panel layer and an electric field, a third component panel composed of a plurality of light amplifying elements each of which emits a primary color emission when simultaneously excited by the emission of said first component layer and an electric field, said light amplifying elements being arranged in groups whereby on excitation of respective light amplifying elements in the same group a different primary color emission occurs. 

1. A display screen comprising a first multielement component panel in which each element thereof is capable of emitting light when selectively activated, and a second component panel adapted to transmit substantially only that light from a selected element and to prevent the transmission of light from non-seLected elements, said second component panel comprising a transparent electrode layer consisting of a plurality of conductive strips, a layer comprising a plurality of associated strips of photoconductive material, each extending substantially right across the respective surface of the second component panel, an opaque conductive layer, a layer of electroluminescent material, and a segmented electrode layer.
 2. A display screen according to claim 1 wherein the first component panel comprises an electroluminescent layer, a first set of conductors on one surface of said layer, a second set of conductors on the opposite surface of said layer, said first and second set forming a selection matrix to permit activation of preselected elements of said electroluminescent material.
 3. A display screen according to claim 1 including an optical filter positioned on one side of said first component panel to remove a predetermined portion of said light.
 4. A display screen according to claim 1 including a third component panel composed of a plurality of light amplifying elements each of which is capable of emitting light when simultaneously excited by light from the respective one of said elected element in said second component panel and an electric field.
 5. A display screen according to claim 3 wherein the third component panel comprises a layer of photoconductive material, an opaque conductive layer, an unbroken layer of electroluminescent material, and an unbroken electrode layer.
 6. A display screen according to claim 4 wherein the second component panel is a sandwich light amplifier for amplifying light produced by a fully selected element of the first component panel, said second component panel having a plurality of diagonally extending, electrically conductive strips passing across the face of the panel whereby, in use, only the light from a selected element in the first component panel is transmitted by the second component panel. 7 A display screen according to claim 6 wherein said conductive strips each comprise a series of substantially square-shaped areas, said areas being each connected to adjacent areas in the same conductive strip at diagonally opposite corners.
 8. A display screen according to claim 6 wherein the second component panel comprises a glass substrate on which are etched tin oxide electrodes to constitute a first set of said conductive strips, a photoconductive layer, an opaque conductive layer, a layer of electroluminescent material, a second set of tin oxide electrodes to constitute a second set of said conductive strips, and a layer of glass, whereby the first and second sets of conductive strips are parallel and on opposite sides of said layer of electroluminescent material to permit selective activation of said strip portions of the electroluminescent material in the second component panel.
 9. A display screen according to claim 1 wherein said electroluminescent layer is a segmented zinc sulfide layer.
 10. A display screen according to claim 1 wherein said opaque conductive layer is adapted to conduct in one direction only.
 11. A display screen for producing a color image comprising a first multielement component panel in which each element thereof is capable of emitting light when selectively activated, a second component panel adapted to transmit substantially only that light from a selected element and to prevent the transmission of light from nonselected elements, said second component panel comprising a transparent electrode layer consisting of a plurality of conductive strips, a layer comprising a plurality of associated strips of photoconductive material, an opaque conductive layer, a layer of electroluminescent material, and a segmented electrode layer, and a third component panel comprising a transparent continuous electrode layer, a layer of strips of photoconductive material, an opaque conductive layer, an electroluminescent layer segmented into strips, and a segmented electrode layer, adjacent strips of said electroluminescenT layer being capable of producing different colors on excitation whereby a composite color image may be produced by the display screen.
 12. A display screen according to claim 11 wherein the strips of electroluminescent material in the electroluminescent layer are strips of zinc sulfide doped with impurities whereby adjacent strips produce said different colors.
 13. A display screen according to claim 11 wherein the strips of electroluminescent material in the electroluminescent layer are strips of zinc sulfide doped with impurities whereby adjacent strips stimulate phosphorescent elements which, in turn, provide the required colors.
 14. A display system including a display screen comprising a first multielement component panel including an electroluminescent layer in which each element thereof is capable of emitting light when selectively activated and a second component panel adapted to transmit substantially only that light from a selected element and to prevent the transmission of light from nonselected elements, said second component panel comprising a sandwich of materials capable of transmitting light from said first component panel on activation of a respective element thereof, said first component panel including a first set of conductors located on one side of said layer and a second set of conductors located on the opposite sides of said layer whereby a selection matrix is formed to selectively develop an electric potential across any required element of said first component panel so that light is transmitted therefrom on activation of the respective element by said potential, said second component panel comprises a glass substrate on which are etched tin oxide electrodes to constitute a first set of said conductive strips, a photoconductive layer, an opaque conductive layer, a layer of electroluminescent material, a second set of tin oxide electrodes to constitute a second set of said conductive strips, and a layer of glass, whereby the first and second sets of conductive strips are parallel and on opposite sides of said layer of electroluminescent material to permit selective activation of said strip portions of the electroluminescent material in the second component panel, circuit means associated with said second component panel to select that conductor in its respective first set and that conductor in its respective second set corresponding to the required portion of the second component panel whereby a potential may be applied thereacross to activate that portion whilst all other portions of the second component panel are retained inactive and means for applying a potential across said portion at the instant that light is emitted from the corresponding element in the first component panel.
 15. A system according to claim 14 wherein said circuits include semiconductor gating circuits.
 16. A color image presentation system comprising a composite panel composed of a first component panel of a luminescent material which when excited to luminescence emits light radiation, a second component panel composed of a plurality of elements each of which will transmit said radiation only when simultaneously excited by the excitation of said first component panel layer and an electric field, a third component panel composed of a plurality of light amplifying elements each of which emits a primary color emission when simultaneously excited by the emission of said first component layer and an electric field, said light amplifying elements being arranged in groups whereby on excitation of respective light amplifying elements in the same group a different primary color emission occurs. 